The present invention ggnerally relates to a communication system and, in particular, relates to such a system having, for each grouping of subscribers, a first apparatus for establishing communication paths interconnecting with a switching network and a second apparatus for establishing communication paths interconnecting with the switching network via a terminal control element associated with the switching network and prededicated to a group of subscribers.
The advent of data communication devices such as computer terminals, high speed printers and numerous other presently known data communication devices has resulted in somewhat of a dilemna for the telecommunication industry.
As well known, most present telecommunication networks are based on conventional analog circuit switched centrally controlled exchanges. One difficulty manifested by such centralized exchanges is that the entire network associated therewith experiences catastrophic failure when a malfunction or failure occurs in the centralized exchange. The occurance of such a failure, regardless of the magnitude thereof, consequently adversly impacts a substantial portion, if not all, of the subscribers thereto. In addition, by being restricted to an analog circuit switched centralized exchange, any data transmission between any two subscribers thereto must traverse the centralized exchange. Further, such data tranmissions are difficult to interfere with and usually require modems to adapt the conventional telephone equipment with the signals required to operate data transmitting/receiving devices. Such modems are becoming more complex and difficult since the variety of data devices, as well as the data rates thereof, is increasing. At the present time, the ideal solution would be to simply install entirely new switching systems, or exchanges that are capable of handling the variety of data types and rates. However, in many instances, such an installation would be quite wasteful since many present exchanges are still not near the end of their useful life.
One alternative to a centralized exchange is a switch network that has distributed control, such as, for example, the ITT System 12 Digital Exchange. In that particular architecture, a plurality of terminal interfaces interconnect with a digital switching network, the digital switching network is provided to establish communication paths between different terminal interfaces. Each terminal interface autonomously sets up communication paths between and among all subscribers connected thereto as well as paths through the digital switching network when a subscriber interconnected to another terminal interface is called. One significant advantage of an exchange having distributed control is that the catastrophic failure of the entire exchange is avoided in the event of the failure of any single component thereof. That is, if one or more terminal interfaces fail those remaining active can still utilize the digital switching network, or in the event that the entire digital switching network fails the terminal interfaces nevertheless provide complete local service to the subscribers thereto.
Since present exchanges are generally adapted to accept only a limited number of different types of devices, it is clear that by providing an exchange having distributed control the expansion thereof, to accommodate all present and future data services, can be modular in nature without requiring the expensive redesign of an entire exchange.
Consequently, it is quite apparent that with the growth and variation of data devices, and the anticipated continued growth of same, some communication system that interfaces with present communication systems and provides substantial data communication services without requiring the elimination of presently existing exchanges is in demand.